1. Field of the Invention
The present invention relates to a dielectric ceramic and a laminated ceramic capacitor, and more particularly, to a dielectric ceramic containing a barium titanate based compound as its main constituent and a laminated ceramic capacitor using the dielectric ceramic, in particular, a small-sized and high-capacitance laminated ceramic capacitor suitable for intermediate to high voltage applications, which has a high rated voltage.
2. Description of the Related Art
Conventionally, barium titanate based compounds which have a high dielectric constant have been widely known as ceramic materials for use in laminated ceramic capacitors. In addition, inexpensive base metal materials such as Ni, which have favorable electrical conductivity, have been widely used as internal electrode materials.
With the development of electronics technology in recent years, a reduction in size and increase in capacitance of laminated ceramic capacitors have rapidly advanced.
This type of ceramic capacitor has a ceramic sintered body obtained by alternately stacking dielectric layers composed of a dielectric ceramic and internal electrodes, and applying a firing treatment, and has external electrodes formed on both ends of the ceramic sintered body. Reducing the dielectric layer thickness and increasing the number of layers stacked allows for the reduction in size and the increase in capacitance of the laminated ceramic capacitors.
Japanese Patent Application Laid-Open No. 2008-162830 proposes a dielectric ceramic composition which has a main constituent including barium titanate, a first accessory constituent containing BaZrO3, a second accessory constituent containing an oxide of Mg, a third accessory constituent containing an oxide of a specific rare earth element R, a fourth accessory constituent containing an oxide of Mn or the like, a fifth accessory constituent containing an oxide of Si or the like, and a sixth accessory constituent containing an oxide of Al, in which the ratios of the respective accessory constituents with respect to 100 mol of the main constituent are as follows in terms of oxide or composite oxide: the first accessory constituent: 9 to 13 mol; the second accessory constituent: 2.7 to 5.7 mol; the third accessory constituent: 4.5 to 5.5 mol; the fourth accessory constituent: 0.5 to 1.5 mol; the fifth accessory constituent: 3.0 to 3.9 mol; and the sixth accessory constituent: 0.5 to 1.5 mol.
In Japanese Patent Application Laid-Open No. 2008-162830, the main constituent including barium titanate contains the sixth accessory constituent in a predetermined amount in addition to the first to fifth accessory constituents, thereby achieving a highly-accelerated life test result of 10 hours or more.